Neutron-proton asymmetry is accounted by \(\delta = (\rho _n - \rho _p)/\rho \)  where \(\rho _n\)  and \(\rho _p\)  are the
density of the neutron and the proton, respectively.
Most of the nuclear structure models fit their model parameters to the nuclear data, and
the constants and coefficients in Eqs.(REF , ) which determine the EoS of nuclear matter are
obtained as results of the fitting.
Among the constants and coefficients in Eqs.(REF , ),
saturation density \(\rho _0\)  and the binding energy \(E_B\)  are determined highly model-independently,
and the values are converged to \(\rho _0=0.16\)  fm\(^{-3}\)  and \(E_B = 16\)  MeV.
On the other hand, compression modulus \(K_0\)  that characterizes the density dependence of EoS in the symmetric nuclear matter
is uncertain more than \(\rho _0\)  and \(E_B\) .
For example, collection of 240 Skyrme force models shows that the models predict the \(K_0\)  value in the range \(200-400\)  MeV [1]}.
Experimentally constrained range is reduced to \(200-260\)  MeV, but it is still uncertain much more than \(\rho _0\)  and \(E_B\) .
Since the average density of a canonical neutron star, a star of mass \(1.4 M_\odot \)  is more than \(2\rho _0\) ,
role of \(K_0\)  in the neutron star matter might be non-negligible and therefore it is needed to reduce the uncertainty of \(K_0\) 
in order to have more exact EoS of the neutron star matter.
Situation is no better than \(K_0\)  for the symmetry energy \(S(\rho )\) .
Ranges of \(J\) , and \(L\)  constrained from experiments are \(30-35\)  MeV and \(40-76\)  MeV, respectively [1]}.
For \(K_{\rm sym}\)  experimental access is still very limited, and the value is guessed from relations with \(L\)  or \(3J-L\) .
Properties of neutron rich systems (\(\delta \simeq 1\) ) are sensitive to the behavior of the symmetry energy.
\(J\) , \(L\)  and \(K_{\rm sym}\)  being siginificantly uncertain, large uncertainty in the EoS of neutron stars is unavoidable.
